FILE - In this Sept. 29, 2013 file photo, Denver Broncos quarterback Peyton Manning watches play from the sidelines against the Philadelphia Eagles in the fourth quarter an NFL football game, in Denver. Manning returns to Indianapolis on Sunday, Oct. 20, 2013, a better quarterback than the one who left. (AP Photo/Jack Dempsey, File)
(The Associated Press)

Denver Broncos quarterback Peyton Manning (18) calls an audible at the line of scrimmage against the Jacksonville Jaguars in the first quarter of an NFL football game, Sunday, Oct. 13, 2013, in Denver. (AP Photo/Jack Dempsey)
(The Associated Press)

Just two years removed from the neck troubles that weakened his right arm but strengthened his resolve, Peyton Manning is off to the best start by any quarterback in NFL history.

He returns to Lucas Oil Stadium on Sunday a much better player than the one who left Indianapolis teary-eyed in 2012 after the Colts let him go in favor of Andrew Luck.

Manning has four terrific targets in Denver to go with the skill, intellect, work ethic and determination he's always had.

With Wes Welker, Demaryius Thomas, Eric Decker and Julius Thomas sharing the catches, the unbeaten Broncos are averaging an eye-popping 42 points a game. Manning has thrown for a record 22 TDs in the first six weeks, and Knowshon Moreno is keeping defenses honest with a league-leading seven TD runs.

Manning loves dissecting defenses and poring over game film but hates digging deep into his own psyche to decipher what makes him tick.

Listen closely to some of his words, though:

"I love practicing every day."

"I'm still learning."

"By no means do I have everything figured out."

This from the four-time MVP who narrowly missed out on a fifth last year.

Most quarterbacks blowing out 37 candles on their birthday cake tire of the tedium of meetings, practices and workouts. They start daydreaming about life after football.

Not Manning.

"Everybody enjoys playing in an NFL football game, but I still enjoy the preparation, the work ... and being effective," Manning said.

Take him out of his comfort zone, put him in a new city with a new team. It's the perfect challenge.

The beauty of Peyton Manning is his beautiful mind.

NBC football analyst Cris Collinsworth said the line he hears most from opponents is "he's playing chess when most of us are playing checkers."

"I think that's really his No. 1 asset," added Tony Dungy, Collinsworth's colleague and Manning's former coach. "He is so smart, he's got such a great memory, such great recall."

Collinsworth said he studies harder for Manning's games than any other ones "because I don't want to look stupid. Because I know that he's going to do something where I'm going to go, 'Now, what just happened there?'"

When John Fox says No. 18 is a fellow coach on the football field, he's not just rattling off another cliche.

Manning's incessant instruction fills Dove Valley during every practice. During training camp, he gave some 1-on-1 tutoring to Montee Ball.

"One day we were out there just me and him and he's yelling things like it's 11-on-11," Ball recounted. "He's pointing out the middle linebacker and yelling at the tight end, changing the call. I look back like, who's he talking to?"

Manning was recreating the entire play for Ball's benefit, including his cadence and pre-snap gesticulations.

He's just as methodical in the film room. Fox leaves the film review to his captains on the day after wins while coaches prepare for the next opponent. So, the Monday morning quarterbacking on offense is handled by the quarterback.

"He basically is running the meeting," receiver Demaryius Thomas said. "You go over the film and he says, 'Everybody, I want you to say what you messed up on. Don't be ashamed.'"

And if somebody doesn't 'fess up?

"Oh, he'll just back up the tape and say, 'OK, what happened here?' And if he hears nothing, he'll back it up again and again until somebody says something," Thomas said. "And if you do say, 'OK, my bad,' Peyton will ask, 'Are you sure? Why? What did you do wrong?'"

It may be uncomfortable at times, but "that allows us to really jell as a team and everyone takes accountability for their play," receiver Eric Decker said. "It helps with communication and camaraderie. The guys really trust in one another. That goes a long way when you're out there on that field."

A football junkie, Manning is consumed by this passion for preparation.

"His focus is on one thing and that's trying to figure out a way to help our team win that last game," offensive coordinator Adam Gase said.

So, when a downpour hit Denver during the fourth quarter of the Broncos' last preseason game, Manning grabbed a ball and started throwing on the sideline. He wasn't warming up to go back in, but "just working on his wet-ball mechanics," Fox explained.

The Broncos didn't retreat to their indoor practice facility during a recent snowstorm but bundled up and went outside in preparation for more cold-weather games like the one last January when the Broncos were upset by Baltimore on a 13-degree night, their only loss in their last 18 games.

Manning is driven by that defeat, and his determination to make up for it shows in his precision passes. He's completing a career-high 76 percent of his throws. Defenses can't double all four of his main targets.

"Somebody's going to be 1-on-1," Demaryius Thomas said. "But Peyton also likes to say, 'I don't care if you do get doubled, you've got to figure some way to get open.' And so I do. We all do. That's the great thing about Peyton. He makes everyone around him smarter."